This invention relates in general to bushings and collet arbors, more particularly of a type adapted for use in computerized numerical controlled (CNC) turning and milling.
In order to update their operations, many machine shops and factory machining operations are converting from prior art types of manually controlled milling machines to what is known in the trade as computerized numerical controlled (CNC) milling machines, in which the relationship between a spindle-rotated tool and a work piece mounted on an adjacent supporting table are completely controlled in accordance with a pre-set computer progam. This may require computerized control of both the speed of rotation and positioning of the tool, and the traverse of the work supporting table in X, Y and Z directions. Furthermore, it requires means for precisely and securely mounting and centering a selected tool in the spindle of the milling machine using a coupling which may be quickly fastened and unfastened to change tools. This function may be performed by collets of a unique shape such as Erickson TG type collets, which are specially designed for this purpose. However, this has the disadvantage of requiring the machine operator, at added expense, to acquire new sets of collets for the CNC milling operations, when he may have many sets of standarized collets in his inventory, such as the 3AT type, which are conventionally useful for many different types of manual drilling, boring and grinding operations, but do not fit onto the spindles of the new CNC type milling machines.
It is therefore the principal object of the present invention to provide an improved type of collet holder, more particularly a collet arbor, which is uniquely designed to adapt collets of a conventional type, such as the 3AT, to be secured to the spindles of CNC type milling machines. A further object of the invention is to provide, in the case of turning or lathe operations, a collet arbor of the type described in which tool changes can be readily effected without unclamping the collet arbor.
These and other objects are achieved in accordance with the present invention in a 4-part composite collet arbor comprising a lamping holder for connection to the milling machine spindle, which may be cylindrical, or alternatively, a tapered holder, which is constructed with an internally screw-threaded socket of restricted diameter along its central axis. The latter accommodates the stem of an outwardly-extended screw having a head of smooth cylindrical outer diameter, the outer end of which comprises a second socket which is internally screw-threaded. The clamping holder has a second internal screw-threaded portion near its outer end which terminates in an annular shoulder. The latter is constructed to accommodate an internal annular shoulder of the stepped, hollow, externally screw-threaded shank of a cylindrical adapter which has an annular external end-flange which has the same outer diameter as the holder, with which it fits flush when the external shoulder of the holder when the adapter is screwed in place in its innermost position. The fourth and outer element of the combination is a cylindrical bushing having an external end flange which is constructed to seat against an internal shoulder of the adapter. The mouth of the bushing is inwardly tapered at a small angle to form an inwardly-directed barrel of reduced diameter. All of the four elements fit together telescopically in coaxial relation, to accommodate a standard collet of the 3AT type, the jaws of which are secured against the tapered interior in the mouth of the last-named bushing. The barrel of the bushing is slotted; and the clamping holder accommodates a set-screw near its outer end which penetrates through its wall into the bushing slot to prevent the combination from rotating about an interposed collet. The screw-threaded inner end of the interposed collet seats in the internally screw-threaded socket in the head of the screw.
It will be apparent that a collet gripped in the combination described can be tightened to securely hold a tool in its jaws by slightly unscrewing the adapter so that if causes the bushing to move forward so that its inwardly tapered mouth compresses the jaws of the collet. The arbor combination is then screwed or otherwise fastened by means of the clamping holder into the spindle of a computerized numerical controlled machine for the milling operation.
If, in the case of lathe or turning operations, it is wished to quickly replace the tool, the adapter can be quickly unscrewed, and rescrewed without unclamping the clamping holder.
The invention, including its objects and advantages will be better understood from a study of the detailed specification hereinafter with reference to the attached drawings.